Symmetric Anion Research Articles

Deciphering the Chemical Bonding in Anionic Thallium Clusters

The chemical bonding schemes of thallium cluster anions commonly comply with neither Wade-Mingos's rules nor the Zintl-Klemm concept and thus far have escaped a fully consistent description. In general, the number of electrons available for the cluster skeleton bonding fall below those required according to the qualitative concepts mentioned and the clusters were labeled "hypoelectronic". Based on fully relativistic band structure calculations on respective complete extended solids and electronic structure calculations on excised, charge compensated, and geometrically optimized clusters, we have identified two mechanisms that are suited to lift the degeneracy of partially filled electronic states and to open a HOMO-LUMO gap, the Jahn-Teller effect and relativistic spin-orbit coupling. Treatment on this level of theory shows that, in accordance with experiment, the thallium cluster anions known are electronically saturated and not deficient in valence electrons. We provide qualitative group theoretical procedures for analyzing the Jahn-Teller effect and spin-orbit coupling in lifting the degeneracy of frontier orbitals in highly symmetric thallium cluster anions.

Potassium trans-[bis(oxalato)diaquacobaltate(II)] tetrahydrate: synthesis, structure, potentiometric and thermal studies

Abstract The title compound, trans-K2[Co(C2O4)2(H2O)2]·4H2O, was synthesised, and characterised by elemental analysis. Acid dissociation constants for the complex were determined by potentiometric titration and calculated by STOICHIO program. The crystal structure of trans-K2[Co(C2O4)2(H2O)2]·4H2O was determined by X-ray diffraction studies. The asymmetric part of the unit cell contains one symmetric anion of oxalate and water molecule bound with Co(II) ion in crystallographic special position, one potassium cation and two molecules of water. Thermal properties of the complex were examined by thermogravimetric analysis (TGA). A decomposition mechanism is proposed on the basis of the results.

A new method to radical anions derived from s-Indacene organobimetallic complexes, their ESR characterization

The following organobimetallic radical anions derived from 2,6-diethyl-4,8-dimethyl-s-indacene (s-Ic′): [CODRh(s-Ic′)RhCOD]− (IIa), [Cp∗Ru(s-Ic′)RuCp∗]− (IIb), [Cp∗Ru(s-Ic′)RhCOD] − (IIc), [Cp∗Ru(s-Ic′)NiCp∗]− (IId) [(CO)3Mn(s-Ic′)NiCp∗]− (IIe) and [Cp∗Fe(s-Ic′)NiCp∗]− (IIf) (COD=1,5-cyclooctadiene; Cp∗=pentamethylcyclopentadienyl) were prepared by reduction of the parent complexes using a monoelectronic transfer from an electron rich olefin. The radical anions were fully characterized by ESR spectroscopy which usually gave a well resolved hyperfine coupling structure, indicating that the spin distribution in the symmetrical radical anions (IIa, IIb) affects mainly the organic spacer whereas in the unsymmetrical ones (IIc–f) it is displaced towards the most electronegative metal center and its ligands. This effect is most pronounced in IId, IIe and IIf. The calculated g tensor values of the radical anions are in good agreement with the experimental values. In heterobimetallic radical anions, the dissymmetric spin distribution shows that the two metals present different electrophile properties leading to potentially different catalytic activities.

Ion-Selective Controlled Assembly of Dendrimer-Based Functional Nanofibers and Their Ionic-Competitive Disassembly

The construction of hierarchical materials through controlled self-assembly of molecular building blocks (e.g., dendrimers) represents a unique opportunity to generate functional nanodevices in a convenient way. Transition-metal compounds are known to be able to interact with cationic dendrimers to generate diverse supramolecular structures, such as nanofibers, with interesting collective properties. In this work, molecular dynamics simulation (MD) demonstrates that acetate ions from dissociated Cd(CH(3)COO)(2) selectively generate cationic PPI-dendrimer functional fibers through hydrophobic modification of the dendrimer's surface. The hydrophobic aggregation of dendrimers is triggered by the asymmetric nature of the acetate anions (AcO(-)) rather than by the precise transition metal (Cd). The assembling directionality is also controlled by the concentration of AcO(-) ions in solution. Atomic force (AFM) and transmission electron microscopy (TEM) prove these results. This well-defined directional assembly of cationic dendrimers is absent for different cadmium derivatives (i.e., CdCl(2), CdSO(4)) with symmetric anions. Moreover, since the formation of these nanofibers is controlled exclusively by selected anions, fiber disassembly can be consequently triggered via simple ionic competition by NaCl salt. Ions are here reported as a simple and cost-effective tool to drive and control actively the assembly and the disassembly of such functional nanomaterials based on dendrimers.

Dicyanoaromatic radical anions as mixed valence species

The reduction of nine symmetric dicyanoaromatic radical anions by sodium amalgam in the presence of cryptand[2.2.2] was studied using cyclic voltammetry and using optical and electron paramagnetic resonance (EPR) spectroscopies in two aprotic solvents. All radicals are charge‐delocalized (Class III) mixed valence species, as shown by the weak solvatochromism of their low‐energy optical bands and by the vibrational structure exhibited by most of the bands. The maximum of the low‐energy optical transition decreases logarithmically with the number of bonds (n) between cyano groups in a series of p‐phenylene‐bridged radicals, from p‐phenyl (n = 5) to p‐quaterphenyl (n = 17), although the energy of the latter lies higher than the value predicted by the linear regression. The energy of this band decreases linearly with the cos2 value of the torsion angle between phenyl rings in the spectra of biphenyl‐4,4′‐dicarbonitrile radical anion and their methyl‐substituted derivatives. The fact that charge delocalization is maintained in radicals with non‐Kekulé bridges, with unusually large bridges and with bridges with highly twisted biphenyl systems suggests that cyano charge‐bearing units have small reorganization energies and induce high electronic couplings through the bridges. Copyright © 2012 John Wiley & Sons, Ltd.

Binary Ionic Liquids with a Common Cation: Insight into Nanoscopic Mixing by Infrared Spectroscopy

Mixing of ionic liquids (ILs) can expand the range of properties and versatility of this new class of solvents. Exploiting this potential requires a fundamental understanding of the mixing behavior of ILs. In this study, we have investigated binary IL mixtures involving a common cation (1-butyl-3-methylimidazolium) with two commonly used anions (chloride, bromide, tetrafluoroborate, hexafluorophosphate or bis(trifluoromethanesulfonyl)imide ([NTf2]−)) by means of IR spectroscopy. Upon mixing the ILs, significant changes in the anion IR bands are induced, indicating mixing at the molecular level for highly symmetric anions. Furthermore, density functional theory (DFT) calculations show water to be a suitable probe molecule: IR bands of anion-1···H–O–H···anion-2, anion-1···H–O–H···anion-1, and anion-2···H–O–H···anion-2 are well suitable for inspection and quantification of the coexistence of each type of cluster. In contrast to some previous spectroscopic investigations, this work suggests good molecular mixing and the absence of nanosegregation in these binary ILs.

Bis(triphenyl-λ5-phosphanylidene)ammonium hydrogen dichloride

In the title compound, [(Ph3P)2N]+·[Cl-H-Cl]− or C36H30NP2 +·Cl2H−, the H atom of the [Cl—H—Cl]− anion and the N atom of the [(Ph3P)2N]+ cation are located on a twofold axis, yielding overall symmetry 2 for both the cation and the anion. The central P—N—P angle [144.12 (13)°] of the cation is in the expected range and indicates only weak cation–anion inter­actions. The almost linear [Cl—H—Cl]− anion is a rare example of a symmetric hydrogen bridge in a hydrogen dichloride anion. The Cl⋯Cl distance and two equal Cl—H bonds are typical of such a symmetric hydrogen dichloride anion.

Understanding the High Solubility of CO2 in an Ionic Liquid with the Tetracyanoborate Anion

The ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate, [emim][B(CN)(4)], shows greater CO(2) solubility than several popular ionic liquids (ILs) of different anions including [emim]bis(trifluoromethylsulfonyl)imide [emim][Tf(2)N]. Herein, both classical molecular dynamics simulation and quantum mechanical calculations were used to understand the high solubility of CO(2) in the [emim][B(CN)(4)] IL. We found that the solubility is dictated by the cation-anion interaction, while the CO(2)-anion interaction plays a secondary role. The atom-atom radial distribution functions (RDFs) between cation and anion show weaker interaction in [emim][B(CN)(4)] than in [emim][Tf(2)N]. A good correlation is observed between gas-phase cation-anion interaction energy with CO(2) solubility at 1 bar and 298 K, suggesting that weaker cation-anion interaction leads to higher CO(2) solubility. MD simulation of CO(2) in the ILs showed that CO(2) is closer to the anion than to the cation and that it interacts more strongly with [B(CN)(4)] than with [Tf(2)N]. Moreover, a higher volume expansion is observed in [emim][B(CN)(4)] than in [emim][Tf(2)N] at different mole fractions of CO(2). These results indicate that [B(CN)(4)] as a small and highly symmetric anion is unique in giving a high CO(2) solubility by interacting weakly with the cation and thus allowing easy creation of cavity for close contact with CO(2).

Tetraethylammonium difluoro(oxalato)borate as electrolyte salt for electrochemical double-layer capacitors

Difluoro(oxalato)borate (ODFB−) is a less symmetric borate anion, which makes it possible to increase the solubility of tetraethylammonium (TEA+) salt in propylene carbonate (PC) and improve the capacitance of electrochemical double-layer capacitors (EDLCs). The use of TEAODFB with PC solvent in EDLCs was investigated in the paper. The results show that TEAODFB has good solubility in PC, and the conductivity is comparable to TEABF4/PC electrolyte. When the molar concentration of TEAODFB reaches to 1.6M, the TEAODFB/PC electrolyte has superior conductivity of 14.46mScm−1 and good capacitor characteristics. Despite the less accessible to the electrode and low energy density was achieved, the specific capacitance of 1.6M TEAODFB/PC electrolyte is 21.4Fg−1 at 1Ag−1, and the energy density and power density were comparable to 1M TEABF4/PC electrolyte at 1–5Ag−1. Temperature characteristic was also tested by 3.3F circular capacitors from −40 to 60°C, the result demonstrates that capacitors using 1.6M TEAODFB/PC electrolyte show much higher capacitance and energy density at the investigated temperatures, and the discharge capacitance of capacitors using 1.6M TEAODFB/PC electrolyte varies with the temperature less than that of 1M TEABF4/PC electrolyte.

Electronic structure and surface properties of the mixed-valence doughnut shaped polyoxomolybdate nanocapsule Mo 57V 6

We report a detailed analysis of the electronic structure and results of molecular dynamics simulations for the large polyoxomolybdate [H 3Mo 57V 6(NO) 6O 183(H 2O) 18] 21− (Mo 57V 6) which is a highly symmetric anion with a complex electronic structure and exhibiting a unique variety of multifunctionality. The six vanadium centres are reduced with one electron each, the six Mo centres are bonded to non-innocent NO ligands and the additional six 4d electrons are mostly delocalised over the rest of molybdenum atoms. DFT calculations carried out with the solvent – modelled by a continuum approach – suggest that despite the large charge of the anion, the Mo 57V 6 framework can be easily reduced in polar solvents. Furthermore, the Mo 57V 6 cluster has 18 water molecules trapped in its internal cavity. Molecular dynamics simulations carried out with different solvent conditions suggest that the water molecules inside the cavity have a high ordered structure over a wide range of temperatures and give important information about the cluster anion interactions with the cations present in solution. The obtained results allow a better understanding of related properties of the giant ball-shaped polyoxometalates/Keplerates as the present cluster contains similar building blocks – like the (metal) 6O 6 type pores with crown ether-like structure.

Vibrational Spectroscopic Studies of Cocrystals and Salts. 3. Cocrystal Products Formed by Benzenecarboxylic Acids and Their Sodium Salts

X-ray powder diffraction, differential scanning calorimetry, infrared absorption spectroscopy, and Raman spectroscopy have been used to study the phenomenon of salt formation in four benzenecarboxylic acids (benzoic acid, phenylacetic acid, hydrocinnamic acid, and 4-phenylbutanoic acid), and in the 1:1 stoichiometric products formed by the cocrystallization of a free acid and a sodium salt. Assignments were derived for the observed peaks in both infrared absorption and Raman spectra of the reactants and their products. In all instances, it was observed that the energy of the antisymmetric stretching mode of the carbonyl group of the free benzenecarboxylic acid invariably shifted to higher energies when that acid formed a cocrystal with a sodium salt of another benzenecarboxylic acid. In addition, the symmetric stretching mode of the benzenecarboxylic acid carbonyl group disappeared in the Raman spectrum of its sodium salt and was also absent in the Raman spectrum of the cocrystal product. It was also found that the antisymmetric carboxylate anion stretching mode, the symmetric carboxylate anion stretching mode, the out-of-plane carboxylate deformation mode, and the vibrational modes associated with the phenyl ring and alkane side chains were not useful spectroscopic tools to differentiate cocrystal and sodium salt, as the observed differences of these vibrational modes did not exhibit significantly consistent differences between the various forms.

Cu(SO3)47-: A Readily Accessible Building Block for New Coordination Polymers

The combination of Cu(II) with excess sodium sulfite or a mixture of sodium sulfite and sodium hydrogensulfite produces a colorless solution consistent with the reduction of Cu(II) to Cu(I). The addition of divalent metal ions such as Mn2+, Co2+, Ni2+ and Zn2+ to such solutions, leads to the generation of coordination networks in which the divalent metal ions link together anions of formula Cu(SO3)47−. This symmetrical anion consists of a tetrahedrally coordinated Cu(I) center bound to the sulfur atoms of four sulfite anionic ligands. Isostructural 1D coordination polymers of composition Na3{[CuI(SO3)4][ZnII(H2O)2]2}·H2O and Na3{[CuI(SO3)4][CoII(H2O)2]2}·H2O, isostructural 2D coordination polymers of composition [Na4(H2O)17][Ni(H2O)6]2{[Cu(SO3)4]2[Ni(H2O)2]3} and [Na4(H2O)17][Co(H2O)6]2{[Cu(SO3)4]2[Co(H2O)2]3}, and a 3D coordination polymer of composition Na(H2O)6{[CuI(SO3)4][MnII(H2O)2]3} are reported.

Hydrogen-bonded supramolecular motifs in crystal structures of trimethoprim barbiturate monohydrate (I) and 2-amino-4,6-dimethylpyrimidinium barbiturate trihydrate (II)

In the present study, we report the crystal structures of two organic salts, namely 2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl)pyrimidinium (TMP) barbiturate monohydrate (TMPBAR) (I), 2-amino-4,6-dimethylpyrimidinium (AMPY) barbiturate trihydrate (AMPYBAR) (II). In both complexes, one ring nitrogen of TMP and AMPY are protonated as a result of proton transfer from the−CH2 group of barbituric acid. In compound (I), the TMP cation and barbiturate anion are paired through twoN−H···O and one N−H···N hydrogen bonds. This pair further self-organizes through N−H···O hydrogen bonds to generate an array of six hydrogen bonds. These arrays are further cross-linked by N−H···O hydrogen bonds forming a sheet-like structure. The water molecule is also embedded in the sheet via O−H···O and C−H···O hydrogen bonds, forming a rosette-like supramolecular motif. TMP cations are also bridged by alternating water molecules via C−H···O and O−H···N hydrogen bonds. In compound (II), the symmetrical barbiturate anions self-organize on both sides through N−H···O hydrogen bonds generating a supramolecular chain. These chains are cross-linked by the three water molecules. A pair of barbiturate anions and two water molecules constitute an array of four hydrogen bonds (DADA quadruple array). These arrays are cross-linked by another water molecule. 2-Amino-4,6-dimethylpyrimidine cations are paired through N−H···N hydrogen bonds. These pairs are bridged by three water molecules generating a supramolecular ribbon. The barbiturate chains and base pairs are arranged in an alternate manner via N−H···O and O−H···O hydrogen bonds to generate a 3-D network.

Direct Calculation of Electron Transfer Parameters through Constrained Density Functional Theory

It is shown that constrained density functional theory (DFT) can be used to access diabatic potential energy surfaces in the Marcus theory of electron transfer, thus providing a means to directly calculate the driving force and the inner-sphere reorganization energy. We present in this report an analytic expression for the forces in constrained DFT and their implementation in geometry optimization, a prerequisite for the calculation of electron transfer parameters. The method is then applied to study the symmetric mixed-valence complex tetrathiafulvalene-diquinone radical anion, which is observed experimentally to be a Robin-Day class II compound but found by DFT to be in class III. Constrained DFT avoids this pitfall of over-delocalization and provides a way to find the charge-localized structure. In another application, driving forces and inner-sphere reorganization energies are calculated for the charge recombination (CR) reactions in formanilide-anthraquinone (FA-AQ) and ferrocene-formanilide-anthraquinone (Fc-FA-AQ). While the two compounds have similar reorganization energies, the driving force in FA-AQ is 1 eV larger than in Fc-FA-AQ, in agreement with experimental observations and supporting the experimental conclusion that the anomalously long-lived FA-AQ charge-separated state arises because the electron transfer is in the Marcus inverted region.

Ab initio study of structures and energies of Al2H4 and Al2H 4 −

The low-lying isomers of Al2H4 and their anions are investigated with the hybrid density functional B3LYP, the coupled-cluster CCSD and CCSD(T) methods, and the electron propagator theory. The positive adiabatic electron affinities 5,798 and 10,112 cm−1 are predicted for the neutral C2v and D2d symmetric isomers, respectively. The D2h symmetric anion is more stable by 852 cm−1 than the C2v symmetric anion. The photodetachment spectra for Al2H4− anions at the C2v and D2h symmetries are simulated on the basis of the Franck–Condon factor calculations, indicating a reasonable way to study the transition state of the intramolecular torsion process

Electron scattering on p-benzoquinone anions

Electron scattering on p-benzoquinone anions was studied in a storage ring and the detachment cross-section measured as a function of electron energy. From a fit to a classical model developed for spherical symmetric anions, the threshold was found at 8.4 eV. According to the electron-binding energy, a much lower value, 4.4 eV, is predicted. The deviation is attributed to neglect in the model of the large polarizability of the π-conjugated anion. Ab initio calculations predict a resonance state below 3 eV but its identification is not within reach of the technique due to the thick repulsive Coulomb barrier.

Synthesis and Structure of [Fc(EtO)PS2]‐ Complexes

AbstractReaction of Fc(S)PS2P(S)Fc with NaOEt gives the non symmetric phosphonodithioato anion [Fc(EtO)PS2]‐ which can be complexed to a range of metal ions. The group 10 metals (Ni, Pd and Pt) adopt [ML2] complexes with square planar coordination. The first known mercury phosphonodithioate complex is shown to adopt a unique dimeric [M2L4] structure. A new structural motif for lead phosphonodithioate complexes is reported consisting of [PbL2] units joined by Pb···S interactions to form distinct dimeric pairs. All new compounds have been characterized spectroscopically and four demonstrative X‐ray structures are reported.

Polymetallated 4‐tert‐Butylcalix[4]arene Complexes of Sodium and Potassium Stabilized by Crown Ethers: Syntheses, Structures and Activation of Carbon Dioxide

Abstract4‐tert‐Butylcalix[4]arene and 18‐crown‐6 react with NaH in THF to form the complex [(18‐crown‐6)(THF)Na4(4‐tert‐butylcalix[4]arene‐4H)]2·3THF (1). Analogously, the reaction with 4‐tert‐butyltetrathiacalix[4]arene in DMF results in the formation of [(18‐crown‐6)Na(dmf)1.5]2[(4‐tert‐butyltetrathiacalix[4]arene‐4H)2Na6(dmf)2] (2) The X‐ray analysis of 1 shows an Na6O6 skeleton consisting of two fused open heterocubanes. Two Na+ ions are encapsulated in the cavities of the calix[4]arene units. Additionally, two peripheral Na+ ions, each surrounded by a crown ether and one THF ligand, are connected to the central Na6O6 skeleton by one bridging oxygen of the calix[4]arene. In contrast, 2 contains the highly symmetrical anion [(4‐tert‐butyltetrathiacalix[4]arene‐4H)2Na6(dmf)2]2− and crown‐ether‐stabilized cations. While 1 shows a dynamic process in solution above 40 °C, the structure of the highly symmetrical compound 2 remains stable at higher temperatures. The solid‐state structure of the potassium complex [(dibenzo‐18‐crown‐6)K4(4‐tert‐butylcalix[4]arene‐4H)(THF)3]2·4THF (4) is similar to 1; however, the calix[4]arene units in the open heterocubane structure of 4 are shifted less than half a diameter to one another than in the sodium complex 1. According to the 1H NMR spectra complex 3a, containing 18‐crown‐6, has a very similar structure to the related complex 4. Both 1 and 4 absorb carbon dioxide in THF and are active CO2‐transfer reagents towards 2‐fluoropropiophenone; complex 2 is much less active. This clearly demonstrates the subtle influence of the structure of the alkali metal complexes on the CO2 reactivity in these types of compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.

Oxygen-17 NMR study of aqueous peroxotungstates.

Aqueous peroxotungstates have been studied from pH 0.5 to 9.0, over a range of peroxide concentrations. Although equilibria are not always established, many anions can be identified by 17O NMR because the ratio of deltaO(W anion)/deltaO(known Mo anion) is consistently 79 +/- 3%. They are [WO3(HO2)]-; [WO(OH)(O2)2]-; [WO(OH2)(O2)2]0; [W2O3(O2)4]2-; [W2O3(OH)(O2)4]3-; [W4O12(O2)2]4-; [W7O23(O2)]6- and [W7O22(O2)2]6-. Their pKa values, where measurable, are about 2 units lower than the corresponding peroxomolybdates, e.g. 0.0 for [WO(OH2)(O2)2]0 and 8.0 for [W2O3(O2)4]2-. Other peroxotungstate species are also present but can only be broadly identified. These include Keggin structures with relatively low peroxo content, and a very unsymmetrical anion appearing at pH ca. 7 that bears no obvious structural relationship to any species previously reported. The main product from the reaction of powdered W metal with 30% aqueous peroxide is provisionally identified as the symmetrical anion [W6O13(OH)2(OH2)2(O2)5]2-, although other minor species are also formed, probably having fewer peroxo substituents.